The present invention relates to a method of driving a laser diode. Recently, for researches in a leading-edge science region using laser light with a pulse duration in the attosecond range or the femtosecond range, ultrashort pulse/ultra-high power lasers have been frequently used. As the ultrashort pulse/ultra-high power laser, for example, a titanium/sapphire laser is known. However, the titanium/sapphire laser is an expensive and large solid laser light source, which is a main impediment to the spread of technology. If the ultrashort pulse/ultra-high power laser is realized through the use of a laser diode, a large reduction in size and price of the ultrashort pulse/ultra-high power laser and high stability of the ultrashort pulse/ultra-high power laser are achieved.
On the other hand, in the communications field, a reduction in pulse widths of laser diodes has been actively studied since 1960's. As a method of generating a short pulse in a laser diode, a gain switching method, a loss switching method (a Q-switching method) and a mode locking method are known, and in these method, a laser diode is combined with a semiconductor amplifier, a nonlinear optical element, an optical fiber or the like to obtain higher power.